We already know that plants have memory and seem to have some form of consciousness. Recently, the Tubingen University, in Denmark, has published the results of a study showing that "plants reveal decision-making abilities under competition". That means they can apply logic in the process, which is a clear sign of thinking by humankind standards. Now, considering that plants have a modular construction, that also means that thinking is not necessarily an ability of a centralized brain, as seen on mammals. We also know that ants, for example, also have some form of collective brain when they farm and store food for themselves and future generations.
The study was published by Nature Communications on 12/21/17.